Social Insect Pheromones: Their Chemistry and Function

Exocrine secretions of social insects are often characterized by extraordinarily complex mixtures of natural products. Thus, chemical communication in social insects must be interpreted in terms of signals generated by multicomponent systems, the individual constituents of which can affect the informational content of the message.Alarm pheromones have been identified chiefly in three subfamilies of ants and their distribution appears to be chemosystematically significant. Myrmicine genera emphasize 3-alkanones as alarm releasers, whereas methyl ketones, primarily of terpenoidal origin, are widely utilized as alarm pheromones in the subfamily Dolichoderinae. Formicine species may employ formic acidas an alarm pheromone in addition to the compounds produced in the mandibular and Dufour's glands. The mandibular gland pheromones are chiefly acyclic monoterpene aldehydes (e.g., citronellal) which are relatively low boiling compounds. Higher boiling n -alkanes are produced in the Dufour's glands and may serve as more persistent releasers of alarm behavior. Alarm pheromones as well as the caste-specific pheromones of male bees and ants, probably also serve as defensive products. In many cases it is likely that pheromones were originally utilized as defensive compounds and their communicative function is a secondary development.